In the public switched telephone network (PSTN), trunk groups are physical facilities used to carry bearer data and signaling between switching offices. Since different trunks and trunk groups are associated with different physical facilities, in the PSTN, features can be defined on a per-trunk-group basis. For example, telecommunications customers can request special features on trunk groups, such as call screening, automatic number identification, and quality of service.
In IP telephony networks, there is no analog to PSTN trunk groups. For example, SIP is used to establish multimedia communication sessions between end users over an underlying IP network. SIP involves exchanging messages between peer entities, referred to as proxy servers, to establish a multimedia communications session between the SIP end users. Unlike PSTN trunk groups where an incoming trunk group can be identified based on the trunk over which a message is received, in SIP, all messages arrive over the same signaling interface. For example, SIP messages are carried over TCP or UDP and all SIP messages arrive at port 5060. Thus, one problem with providing trunk-group-like features in a SIP network includes identifying an incoming signaling trunk.
Another problem with using SIP to create to PSTN-trunk-group-like features is that even if the trunk group can be identified, the SIP protocol specification does not specify methods for providing PSTN-trunk-group-like features.
Accordingly, there exists a long felt need in the industry for methods and systems for identifying SIP trunk groups and for selectively processing calls on a per-trunk-group basis.